Fast acting current switch



May 22, 1962 T; H. BATZER ETAL 3,036,172

FAST ACTING CURRENT SWITCH Filed Oct. 14, 1960 2 Sheets-Sheet 1 J Tl woatis TIME, milliseconds INVENTORS THOMAS H. BATZER JAMES F RYAN DAVID B. CUMMINGS BY W 4 6/ ATTORNEY FAST ACTING CURRENT SWITCH Filed Oct. 14, 1960 2 Sheets-Sheet 2 INVENTORS THOMAS H. BATZER JAMES 1 RYAN DA WD 8 CUMMINGS ATTORNEY United States The present invention relates generally to a high current electric switch and more particularly to a fast-acting fluid-operated electric switch capable of handling extremely heavy currents with a. minimum of arcing.

There are countless numbers of electric switches available at the present time, both commercially and for special application in the field of scientific research. There are, on the other hand, few switches that are capable of closing a circuit carrying current of the order of 100,000 amperes for periods of time in excess of milliseconds. An ignitron electronic switch, for example, is capable of switching high currents lasting less than 5 milliseconds and has the added advantage of a very short rise time. This same ignitron, however, when subjected to high currents for durations of /2 second will burn out after one or two operations. In order to handle large currents for /2 second or more many ignitrons must be paralleled to bring the individual currents through each ignitron down to their rated capacity. This in turn involves complex electrical circuitry and the added expense of installing and maintaining many ignitron tubes. On the other hand, there are many mechanical switches, i.e., power circuit breakers, which handle very high currents but are slow acting, awkward and usually of semi-manual operation. Such switches are generally bulky and of special design in order to withstand the inevitable arcing.

To overcome the problems associated with precise high current switching with a minimum of arcing the present invention provides an improved mechanical switch which is preferably employed in combination with an ignitron switch to accomplish the desired switching junction. The ignitron is used to initially close the circuit because of its fast rise time and shortly thereafter the mechanical switch of the present invention is closed and the current bypasses the ignitron. The arcing which normally exists when closing mechanical switch contacts in a high current circuit is minimized in the present invention by a unique switch design wherein the contacts are rapidly closed by means of a differential pressure air cylinder.

Therefore it is an object of the present invention to provide an improved high current switch capable of closing an electrical circuit that delivers of the order of 100,000 amperes.

It is another object of the present invention to provide a fast acting switch wherein arcing is minimized resulting in increased switch lif It is yet another object of the present invention to provide a switch capable of handling high currents for time durations well exceeding 5 milliseconds.

A further object of the present invention is to provide an improved switch with built-in safety features wherein such switch and safety features are easily synchronized with an exterior circuit.

Further features and method of operation of the present invention, together with other objects and advantages thereof will become apparent in the following description considered in conjunction with the accompanying drawings of which:

FIGURE 1 is a simplified schematic diagram of a typical circuit employing the switch of the present invention;

FIGURE 2 is a graph showing the current rise and decay in the circuit shown in FIGURE 1;

atent 0 FIGURE 3 is an elevational sectional view of the switch of the present invention;

FIGURE 4 is an enlarged fragmentary sectional view taken along line 4-4 of FIGURE 3;

FIGURE 5 is an enlarged fragmentary detail view broken out of FIGURE 3 of the seating configuration for the differential pressure drive piston of the switch; and

FIGURE 6 is an enlarged fragmentary sectional view taken along line 66 of FIGURE 3.

In the fields of nuclear research, electronics, and elsewhere, it is often desirable to switch large amounts of current in a short period of time. For example, in connection with various devices for confining and raising gas in the ionized state, viz., as a plasma, to high kinetic temperatures whereby nuclear reactions productive of neutrons in copious quantities may be made to occur between the plasma constitutents, it is necessary to generate magnetic fields of extremely high intensity. To generate these magnetic fields, which generally vary from 1 to 200 kilogauss, large currents from capacitor banks are discharged through low inductance coils. The coils are specifically designed for the particular magnetic field configuration desired. To provide continuity in the circuits handling the above large currents, special fast-acting switches with high current capacities, and long life are required.

The present invention provides a switch which may be advantageously utilized in such a high current circuit, and more particularly which is herein embodied with an ignitron switch to provide electrical continuity between, for example, a 10 joule capacitor bank and a coil producing from 10 to 40 kilogauss as used to generate the magnetic confinement field of a plasma confining and heating device of the type known in the magnetohydrodynamic and plasma physics arts as a mirror machine or Pyrotron. A general description of such a device may be found in Project Sherwood, Amasa S. Bishop, Addison-Wesley Publishing Co., Inc., Reading, Massachusetts, U.S.A., 1958, and is accordingly not detailed herein.

Considering the invention now in some detail and referring to the accompanying drawings thereof, and in particular t-o FIGURE 1, there is shown a simplified schematic circuit as employed for establishing the magnetic field in a mirror machine device. A capacitor bank 11 is charged to the desired voltage by an exterior power supply (not shown). The bank 11 is connected in series to a solenoid coil 12 where coil 12 is of such dimensions and configuration as is necessary to provide the desired magnetic mirror confinement field for non-materially confining a gaseous plasma. A series electronic ignitron 13 is disposed in series with the bank 11 and coil 12 to rapidly close the circuit thus allowing bank 11 to discharge through coil 12. As the current in the coil reaches its peak positive value a shunt (crowbar) circuit comprising crowbar electronic ignitron 14 disposed in parallel with the coil is conventionally triggered thus providing a short circuit across the coil and maintaining the peak field intensity for a relativ ly long period of time determined substantially by the L/ R decay of the coil. The short circuit path through the crowb-ar circuit allows passage of the current stored within the coil without applying a significant reversal of voltage across the capacitor bank 11, where such a voltage reversal would be injurious to the bank. In turn crowbar ignitron 14 is not capable of handling the high current within the short circuit path for the period of time necessary to match the L/R decay time of the coil. Therefore a switch 15 in accordance with the present invention is connected in parallel with the ignitron 14 and coil 12 and is closed at the proper time to bypass and thus relieve the ignitron 14 of the high current. To reduce the How of current between the switch contacts due to arcing prior to closure a saturable reactor 16 is disposed in series there- Q with. It is noted that although single ignitrons are herein referred to (as ignitrons 13 and 14) in the interest of simplicity of description, it is appreciated that due to the high currents employed in the circuit of FIGURE 1, a

plurality of ignitrons are actually used to comprise such ignitrons 13 and 14.

The operation" of the switch of the present invention in relation to its specific employment in the circuit of FIG- URE 1" is best understood by referring now to FIGURE 2. The high current that is obtained by discharging the capacitor bank 11 rapidly through coil 12 by means of series ignitron I3 is represented by a sinusoidally rising curve 17, which curve reaches a peak value in approxirnately /2 millisecond. Normally the currentwould diminish in a sinusoidal curve 18, which, as mentioned before, would cause a large voltage reversal in the bank 11 thus damaging it. To prevent the reversal, at the peak current value the crowbar ignitron 14 is conventionally 'fired causing the current to decay as curve 19. As is well known in the art, ignitron switches that carry large loads for a long interval have a short life. Thus, the mechanical switch 15 is timed to close approximately 500 microseconds after current curve 17 reaches its peak value. Point 21 represents the time when switch 15 is closed. Curve 22 represents the current decay in the ignitron 14 and curve 23 represents the current rise in switch 15 without the saturable reactor 16. Curve 24 shows the delay impressed upon the current rising in the switch 15 with the addition of the saturable reactor 16. After the switch 15 closes the current continues to decay along a cu'rve'lil, which diminishes slower than curve 19 and is specifically dependent upon the inductance in the circuit and the lesser resistance of the mechanical switch 15.

Although the corresponding voltage curve 25 drops slightly below the abscissa and is negative after the current curve 17 peaks, this slight reversal is not great enough to damage capacitor bank 11. After the slight reversal the voltage decays slowly to zero as shown by curve 26. In view of the foregoing it will be appreciated that in such application, the switch 15 must be extremely fast acting, capable of carrying very high currents for a sustained period of time, and possess a longlife. To these ends, the switch 15, as illustrated in FIGURE 3,preferably includes a cylindrical housing 27 containing-an electrical' con-tact assembly 28 wherein a movable contact thereof is affixed to and moved in a reciprocating linear manner by a differential-pressure air-driven piston assernbly 29. To absorb the acceleration imparted to the piston and contact, a novel buffer assembly 3-1 is provided. As important adjuncts to the switch for the Specific employment depicted in FIGURE 1, a solenoid driven safety lock 32 may be provided to prevent the switch 15 from closing until such time as the capacitor bank 11 is charged to the desired voltage. In addition, a RF signal coil 33 may be advantageously included as an integral part of switch 15 to provide a signal means for synchronizing the switch and associated circuitry of FIGURE 1'. Partial travel of the switch results in a signal pulse from the coil 33 where such signal pulse is thereupon used to trigger the series ignitron 13 as described supra. A cycle switch 34 is also best included to provide ameans for indicating when the switch 15 has re-opened and is ready to fire again. At such time that the switch does not fully re-open and is therefore not ready to "fire, the switch 34 will give indication thereof and proper measures may be taken to overcome the failure. I

The'cylindrical housing 27 extends the full length 0 7 the switch 15. In order that the switch components may be readily assembled, and sincepart of the housing must be non-conductive, the preferred construction of housing- 27 is to couple together by flanges and bolts or other suitable means a series of suitable cylinders. The cylin ders are so arranged and of such length as to permit relatively simple access to a desired component within the housing with a minimum of disassembly thereof. More particularly, in the preferred embodiment the housing 27 is formed of non-conducting cylinders 36 and 37 and metal cylinders 38 and 39.

Cylinder 36 preferably comprises an outer cylindrical member 41 constructed of a fibrous-glass and thermosetting plastic resin or equivalent insulating material, each end of which is flared outward to form similar flanges 42. To strengthen the flanges annular metal rings 43, shaped to fit the flare of the flanges 42, are bonded thereto. One flange 42 is affixed to a circular centrally-apertured upper bus plate assembly 44, which comprises several plates of diminishing diameters atfixed one to the other thus closing off the upper end of cylinder 36. An elongated tube 46 has one end thereof welded 'coaxially to the top side of assembly 44, the other end thereof being rigidly attached by suitable fastening means such as a threaded assembly 4 7, to a safety blow-out device such as a diaphragm 48. V a

The opposite flange 42 and bonded metallic ring 43 of cylindrical member 4-1 are bolted through a lower circular bus plate 491w a bonded metal ring 51 and a flared flange 52 of an outer member 53 of the cylinder 37 the member 53 being similar in design and material to member 41 but of different length. The entire lengths of members 411 and 5-3' are lined with an inner cylindrical insulatin'g" member 54 of a composition, for example, such as Shell Chemical emu-82 8 Cylinder 37 is in turn flanged and bolted to the metal cylinder 38 which in turn isflanged and bolted by suitable means to the metal cylinder 39. More specifically, the lower flange of cylinder 38 is bolted to a feedthrough spider plate 56 the lower surface of which has an annular groove machined therein to receive the upper end of cylinder 39. ,1 The cylinder 39 is held in place by means of exterior tie rods 57 which extend through the lower flange of cylinder 38 and also through a circular cover plate 58 fitted to the bottom end of cylinder 39. Pressure seals are provided in the form of O-rings between the various cylinders and plates throughout the housing 27, to prevent air leakage from the housing to the outside and between various portions of the housing.

contact, on plate assembly 44, and in the case of the lower contact, on lower bus plate 49. The other end of each contact array 61 isslotted along its length and to the flange to form a plurality of separate circumferentially spaced contact fingers 62. Each of the fingers has silverbrazed theretoa contact shoe 63, preferably of a silvertungsten composition. It is generally known in the art that a high current electrical contact formed of a plu: rality of independent contact elements bearing against a solid contact provides an optimum amount of surface contact therebetween in comparison to other designs. To

maintain the flexible fingers of the present invention continually in compression and insure a good bearing action a thick semi-elastic'rubber band 64 is circumferentially' placed about the ends of the fingers 61I The rubber band 7 64 is in turn firmly restrained by a metal band 66 disposed concent'rically thereabout, I

' Contact assembly 28 also includes a movable cylindrical contact'67 which is arranged to travelcoaxially into and out of contacting and bridging engagement between the contact shoes 63 of stationary contacts 59, 59'. The contact 671 preferably comprises a series of copper-tungsten rings silver-brazed end to end and mounted by suitable means including radial spiders 68 to an axiallyex tending,non-conducting drive shaft 6h. To strengthen the contact 67 the serie's of brazed rings are kept in compression by such mounting means. Inasmuch as there would normally be a severe tendency for arcing to occur between the movable contact 67 and fingers of the fixed contacts 59 and 59, a cylindrical insulating sleeve 71 is mounted concentrically within the fingers of each fixed contact with the shoes 63 projecting inwardly beyond the sleeve. In this manner the outer surface of movable contact 67 and only the shoes 63 of the fixed contacts are held in slideable engagement by the rubber rings 64.

At such time as movable contact 6-7 is operated to the closed position it provides electrical continuity between the stationary lower contact 59 described above and the opposite identical stationary contact 59' coaxially mounted on upper bus plate assembly 44. Movable contact 67 is guided into the upper stationary contact 59' with a minimum of finger chatter therebetween by a guide rod 72 attached to the upper end of drive shaft 69, such rod 72 extending upwardly through a bushing mounted axially in the assembly 44 and into the tube 46. To facilitate electrical connection of the switch in a circuit such as that of FIGURE 1, a plurality of coaxial cables 73 are arranged about the periphery of bus plate assembly 44 and plate 49 whereby bus plate 49' connects to the inner conductor and assembly 44 to the outer conductor of each of the cables.

Considering now the piston assembly 29 for moving the contact 67 into bridging engagement with contacts 59, '59, it is to be noted that this assembly includes an air actuated drive piston 74 having a rigidly attached shaft 76 extending coaxially therethrough, the upper end of the shaft being secured to the lower end of the contact drive shaft 69 as by means of an aluminum sleeve 77. The drive piston is formed of a light metal, e.g., aluminum alloy, and is fitted to slide within metal cylinder 38 when actuated by a differential pressure system further described below.

As best shown in FIGURE the piston 74 has an annular groove 78 machined in its lower surface for engagement with a metal seat ring 79 secured in pressure sealed relation within cylinder 38. The ring is supported upon a spacer sleeve 81 which is in turn supported concentrically within cylinder 38 upon spider plate 56, and the ring is secured to the spider plate as by means of threaded fasteners 82 extending therebetween (FIGURE 3). The ring has an upwardly projecting annular rib 83 facing the groove 78 such that when the'piston 74 seats against the seat ring 79, annular groove 78 fits over the annular rib 83. The dimensions of the groove and matching rib are such as to allow the placement of air seal O-rings 84 and 86 in the inner and outer annular spaced formed between smaller and larger circumferences respectively, of the groove 78 and rib 83. O-rings 84 and 86 are held in place by means of O-ring keepers 87 and 88 respectively mounted in slots formed in the inner and outer circumference of rib 83. A small annular groove 89 is machined into the face of rib 83 to provide a small volume or space between the O-ring seals 84 and 86 where one wall of such annular groove 89 is defined by the lower surface of the drive piston 74. Several passages 91 for incoming air are provided in communication with the groove 89 at circumferentially spaced locations therealong. Such passages preferably extend downwardly from the groove and then radially outward through the ring 79 and cylinder 3'8. Groove 89 and passages 91 are used to pass high pressure air therethrough, the combination acting as a means for triggering the diflerential pressure piston 74 in a manner detailed hereinafter relative to the operation of switch 15. As mentioned hereinbefore, a safety lock 32 may be advantageously included in the switch to prevent premature closure thereof and such lock is best provided as a lock-out body 92 bolted to the underside of annular ring 79 and arranged to lock the drive piston 74 in the ready position. As is seen from FIGURE 6 in conjunction with FIGURE 3, a rectangular lock-out slide 93 is mounted for sliding translation within the body 92 and has a keyhole-shaped passage 94 to allow the metal buffer shaft '76 secured to the piston and drive shaft 69 to pass therethrough. A shoulder 96 on shaft 76 presents a diameter larger than the smaller part of the keyhole passage 94; thus when slide 93 is in the lock position, movement of the interconnected shafts 69 and 76 and the piston 74 is prevented. A solenoid 97 is connected by a rod 98 extending in sliding relation through cylinder =38 into attachment with lock-out slide 93 such that by energizing the solenoid the slide is positioned so as to present to the shoulder 96 the larger portion of the keyhole passage 94. This larger portion permits passage therethrough of the shoulder 96 and the integral shafts and piston. Solenoid 97 is appropriately mounted by means such as a clamp or bracket 99 to the lower flange of cylinder 38. A guide rod 101 identical to drive rod 98 is attached to the opposite side of lock-out slide 93, and extends through cylinder 38 to present identical pressure surfaces on either side of the slide and to act as a guide to prevent binding thereof.

The buffer shaft 76 extends downwardly through the center of plate 56 into the air bulfer assembly 31.

The preferred structure of the buffer assembly 31 which is disposed within cylinder 39 comprises a thin buffer piston 162, preferably of aluminum alloy, secured to the buffer shaft 76, such shaft extending downwardly from piston 74 and slideably traversing spider plate 56. The piston 102 is disposed so as to slideably travel within a ported cylinder 103' which extends the length of the piston stroke and which is rotatably secured to a buffer vessel 104 secured within cylinder 39. A retaining flanged ring 105 may be used to rotatably mount the cylinder 103 to vessel 184 and the upper end thereof is flanged for bolted attachment to the undersurface of plate 56 with the lower end of the vessel extending downwardly over the ported cylinder 10 3 to cover the upper ports 106 arranged about the circumference thereof. Between the vessel 104 and ported cylinder 103 there is snugly fitted a concentric ported sleeve 107 which sleeve is integrally connected to vessel 104 by means of a set screw 108. The ported cylinder 1103 may be rotated within the sleeve and vessel to vary the size of the upper ports 106 and regulate the amount of buffer cushioning offered by the assembly 31 in a manner detailed hereinafter.

As regards the RF signal coil 33 and cycle switch 34 of previous mention, their actuation is best effected by means of a trigger rod 109 coupled to shaft 76. In this connection, the lower end of shaft 76 is drilled to receive the upper end of the trigger rod 109, the latter extending downwardly through a seal in the center of cover plate 58 to butt against and thus close the cycle switch 34. Rod 189 also passes within the RF pickup coil 33 whereby a movement of the rod at such time as the switch 15 is closed creates a trigger pulse in the coil, which pulse may then be used to synchronize the switch and accompanying high current circuit. More particularly coil 33 is disposed about a cylindrical portion of an adjustment plate 111, through which rod 189 passes. Plate 111 is threadably mounted on support rods 112 so as to permit varying the distance from coil 33 to the lower end of the trigger rod 109, the upper ends of support rods 112 being secured to a support base 113 at the underside of cover plate 58. The lower ends of rods 112 are secured to a support plate 114 upon which the cycle switch 34 is mounted as by means of a bracket 116.

An external valve system is provided for triggering the switch 15 and repressurizing various internal portions thereof, namely, a high pressure chamber 117 defined between the undersurface of the piston 74 and the cover plate 58, a low pressure chamber 118 defined between the upper surface of piston 74 and a non-conductive partition plate 119 spaced slightly downward from bus plate 49, and an arc suppression chamber 121 defined between plate 119 and upper bus plate assembly 44. The valve system comprises a first three-way solenoid-driven valve 122 dis- V 118 and 117 are given by spear/a posed so as to introduce high pressure air from a source (not shown) to the high pressure chamber 117. A second three-way solenoid driven valve 123 is disposed to introduce when desired high pressure air from the air line between valve 122 and high pressure chamber 117, to the passages 91 in the differential pressure piston assembly 29. Both valves 122 and 123 are vented to the atmosphere by means of outlets 124 and 126 respectively.

Air is introduced at a constant low pressure through a passage 127 drilled through the wall of the cylinder 37 and through partition plate 119 to enter low pressure chamber 118. Similarly, a double passage 128 drilled through the cylinder 37 and plate 119 provides a means for introducing air at a constant high pressure into arc suppression chamber 121.

in actual operation of the switch as employed in the circuit of FIGURE 1, the following sequence of operations occurs. At such time as the lock-out slide 93 is in the locked position (indicated by the cycle switch 3'4) activating a start switch (not shown) places the solenoid air valves 122 and 123 in the opened and closed positions respectively, and high pressure air enters the high pressure chamber 117. Simultaneously the bank 11 is charged to the desired voltage; such action being impossible until slide 93 is in the locked position; that is, till cycle switch 34 is closed. At such time as the bank 11 is fully charged, a signal is sent therefrom to activate the lock-out solenoid 17 which solenoid moves rod 18 and thus slide 93 to the unlocked position previously described. Movement of rod 98 in turn closes a switch (not shown) which activates thesolenoid air valve 123. With operation of valve 123 high pressure air enters the annular groove 89 in rib 83 by way of passages 91, forcing piston 74 upward away from the seat ring 79 and off the O-n'ngs 84 and 86. The instant the piston 74 lifts off O-ring 84 there is a much greater piston area upon which the high pressure acts and the piston 74 is rapidly driven against the oppos- 7 ing low pressure air of chamber 118.

After piston 74 is triggered by air from valve 123 and begins to move, the corresponding movement of trigger rod 109 induces a current signal in the coil 33. As previously mentioned, as the switch 15 continues to close the signal from coil 33 initiates closure of the series ignitron 13 (FIGURE 1) which allows the capacitor bank 11 to discharge into coil 12. Simultaneously the signal from coil 33 triggers a conventional delay circuit (not shown) which initiates closure of the parallel crowbar ignitron 14 a predetermined time after the closure of ignitron 13 as per previous explanation. In turn a predetermined time after ignitron 14 closes, the, contacts of the slower moving switch "15 close, relieving ignitron 14 of its high current load. a

After the current decays through coil 12 and the switch 15, the valves 1'22 and 123 are reversed venting the high pressure air to the atmosphere. The piston 74 and movable contact 67 are thereupon returned to the open position by the low pressure air in chamber 118. When piston 74 seats into ring 79, integrally connected buffer shaft 76 and shoulder 96 travel downwardly inside keyhole passage 94- of slide93. Slide 93 is spring loaded so as to present the small opening of keyhole passage 94 against the shoulder '96 at such time as the shoulder passes thereunder.- Piston 74 is thereupon locked in place and trigger rod 109 closes the cycle switch,34. A conventional indicator'circuit (not shown) indicates that the switch 15 v has finished the cycle and is locked in place. At this point the sequence of operation of switch 15 and assoclated circuitry may be repeated by closing the start switch whereupon valve 122 opens repressurizing chamber 117, bank 11 is charged to the desired voltage, etc. 7

, In keeping with the concept of the differential pressure piston type of operation of the switch of the present invention, the relative pressures supplied to the chambers L B HX H where P gauge pressure in low pressure chamber 118; P gauge pressure in high pressure chamber 117; A area acted upon by low pressure; and A =area acted upon by high pressure.

In actual operation, in order to overcome any fluctuation in air pressure, P XA is normally made larger than P XA in order to provide a good seating of piston 74 on seat ring 79'.

The reservoir volumes contained in the low pressure chamber 118 and the high pressure chamber 117 are so selected that P =P at the end of the piston stroke. If P is low at the end of the stroke or if the reservoir volume is too low, reversal of pressure will occur which will cause oscillation of the piston 74. On the other hand, too much volume will increase the size and bulk of the subject switch. Thus for equal given pressures at the end of the stroke for the least total volume V V' there follows that 'H-b 's V'L where: V =initial volume high pressure chamber 117; V =initial volume low pressure chamber 118; and V =swept volume of stroke.

shock. This is done by the novel air buffer assembly 31 a which necessarily involves little friction and is of light weight so as not to detract from the speed with which the switch is closed. After the start of the stroke the bufier piston 102 travels freely; the wide lower ports in the port-ed cylinder 103 allow air to escape therethrough. At about 40% of the stroke travel the lower ports end and air is trapped in front of the piston 102 within the volume defined by cylinder 103 and buifer vessel 104. This trapped air is com-pressed until the required retarding pressure is reached. Thereafter the upper ports 106 are exposed to'the buffer piston 102 and the compressed air is allowed to flow from in front of the piston 102 around the'edges thereof and into the volume behind the piston, this volume being chamber 117. Thus air is allowed to flow from a high to a relatively low pressure side of the piston 102 as mentioned supra. Such flow may be varied by varying the size of the upper ports rotating ported cylinder 103 with respect to the concentric, similarly ported sleeve 107 disposed within vessel 104. Such variable upper ports are desirable in order that they may be easily adjusted to hold a constant pressure and thereby constant retarding force against piston 102 for the last part of the piston stroke. In the present invention, therefore, the

upper ports are of such accumulative size as to equate vention except insofar as defined in the following claims.

' means coaxially mounted within and insulated from said housing, second stationary contact means coaxially What is claimed is: g 1. In a high current electric switch, the combination comprising a cylindrical housing, firststationary contact mounted within andinsulated from said housing opposite to and insulated from said first contact means, said .first and second stationary contact means each including a cylindrical array of flexible'contact fingers, movable con tact means concentrically disposed 'within the cylindrical array offleXible contact fingers of said second contact means to slidably engage the cylindrical array'offlexible contact fingers of said first contact means, anddiifer'ential pressure drive piston means disposed within said housing and coupled to said movable contact means to selectively impart rapid linear motion thereto and drive same into slidable engagement with said first contact means.

2. The combination according to claim 1, further comprising shock cushioning air buifer means coupled to said drive piston means to decelerate same to a stop at the end of travel thereof in engagement with said first contact means.

3. In a high current electric switch the combination comprising a cylindrical housing, first cylindrical stationary contact means mounted within and insulated from said housing, second cylindrical stationary contact means mounted within and insulated from said housing in coaxially spaced insulated relation to said first stationary contact means, cylindrical movable contact means concentrically mounted within said second contact means and sildable therein into engagement with said first contact means, a circular drive piston coupled to said movable contact means and slidably disposed within said housing, means defining high and low pressure chambers within said housing on opposite sides of the piston with the piston defining a movable dividing wall between said pressure chambers, seating means disposed within said high pressure chamber for mating with and decreasing the surface area of said drive piston exposed to the high pressure chamber when the piston is firmly seated on the seating means, valve means for introducing air to said chambers and establishing a predetermined pressure differential between said high and low pressure chambers conducive to acceleration of the piston in the direction of the low pressure chamber and towards the first contact means when the total cross surface area of the piston is exposed to the high pressure chamber, and trigger valve means for selectively applying sufiicient air pressure to said piston to initiate movement thereof off of the seating means.

4. The combination according to claim 3 wherein said piston has an annular groove in its face exposed to the high pressure chamber and said seating means comprises an annular seat ring fitted within said high pressure chamber, an annular rib formed on said seat ring and extending toward said drive piston for snug mating engagement with said groove therein when the piston is in seated position, an annular trigger groove machined into the face of said annular rib whereby the upper side of said groove is defined by the lower surface of said drive piston when seated, and means communicably connecting said trigger groove to said trigger valve means to provide a burst of high pressure air to the trigger groove for unseating said drive piston from said seat ring.

5. The combination according to claim 3 wherein said first and second stationary contact means comprise opposed cylindrical contact arrays, each array comprising a hollow conducting cylinder secured at one end to said housing and uniformly longitudinally slotted at its other end to form a plurality of circumferentially spaced semiflexible fingers, a contact shoe rigidly mounted on the inner side of the end of each finger, a cylindrical insulating sleeve concentrically disposed within and extending the length of said cylinder into end abutment with said shoes, and resilient means disposed about the circumference of the ends of said fingers to place a radially inward stress thereon.

6. The combination according to claim 3 wherein said cylindrical movable contact means comprises a series of aligned copper tungsten rings silver brazed together, and mounting means maintaining said rings in axial compression.

7. In a high current electric switch the combination comprising a cylindrical housing, first and second cylindrical stationary contacts disposed in coaxial spaced opposition within the upper end of said housing, means defining an arc suppression chamber in the upper end region of the housing enclosing said contacts and sealed from the remainder of the housing, a cylindrical movable contact concentrically disposed within said second stationmy contact and axially slid-able therein into engagement with said first stationary contact to conductively bridge the space therebetween, a drive shaft secured to said movable contact and extending in hermetically sealed relation from the arc suppression chamber into the remainder of the housing, a drive piston slidably disposed within the remainder of the housing and aflixed to the end of said drive shaft opposite said movable contact, said piston having an annular groove in its under surface, means defining high and low pressure chambers in the remainder of said housing on opposite sides of the piston, an annular seat ring concentrically mounted within said high pressure chamber and having an annular rib protruding therefrom for sealed seating engagement with the groove in said piston whereby the piston area exposed to said high pressure chamber is substantially reduced at such time as said piston is seated upon said seat ring, a buffer shaft rigidly aflixed to said piston and extending coaxially into said high pressure chamber, an inverted cylindrical buffer vessel coaxially secured within said high pressure chamber and traversed by said buffer shaft, having a cylindrical member rotatably mounted within said vessel and a set of upper ports covered by the vessel and a set of lower ports disposed below the lower end of the vessel, a concentric sleeve disposed between said cylindrical member and said vessel and firmly affixed to said vessel, said sleeve having ports conforming to said set of upper ports and circumjacent same whereby the size of said upper ports may be varied by rotating said cylindrical member with respect to the integrally combined vessel and sleeve, a buffer piston slidably mounted within said cylindrical member and secured to said buffer shaft, a trigger rod axially aiiixed to said buffer piston and extending therefrom to protrude through the lower end of said high pressure chamber, signal means including an RF. coil secured to the lower end of the housing and disposed about the protruding end of the trigger rod, cycle indicating means including a cycle switch disposed to actuatingly receive the end of said trigger rod when the drive piston is seated upon said seat ring, lock-out means including a solenoid for preventing motion of said drive piston until a predetermined triggering time, air source means communicably connected to said suppression chamber and high and low pressure chambers, solenoid air valve means disposed between said air source means and Said chambers to selectively introduce air thereto and establish a greater pressure in said high pressure chamber than in said low pressure chamber, and a solenoid trigger valve communicably connected between said air source means and the face of the seating ring rib to selectively introduce a burst of air thereto at said predetermined triggering time, said burst of air initiating movement of the drive piston off of said seating ring to expose the total surface of the underface of the piston to the pressure of the high pressure chamber.

8. In a high current electric switch, the combination comprising a cylindrical housing, first stationary contact means coaxially mounted within and insulated from said housing, second stationary contact means coaxially mounted within and insulated from said housing opposite to and insulated from said first contact means, movable contact means concentrically disposed within said second contact means to slideably engage said first contact means, differential pressure drive piston means disposed within said housing and coupled to said movable contact means to selectively impart rapid linear motion thereto and drive same into slideable engagement with said first contact means, an outer cylindrical vessel secured in coaxial depending relation to said diflierential pressure drive piston means, an inner cylindrical member concentrically disposed within and extending beyond the lower end of said vessel and rotatably mounted therein, said member hav- 111 ing an upper and; a lower set ofports therethrough with the upper set of ports covered by the. vessel and the lower. set of ports disposed below the lower. end of said. vessel, a

sleeve disposed between said vessel and said member and.

having ports conforming to, said upper ports, said sleeve rigidly connected to said outer vessel-with its ports in cir= cumjacent relation to said upper ports whereby the size of; said upper eombinationof ports; isvariable by rotation. of said member relative to said vessel, and a circular buffer piston slideably fitted within, said inner member 10 V 12 and. coupled; to said; drive piston; means to travel in; slide.- able reciprocating motion. therewith;

References Cited: in the file. of this, patent UNITED STATES PATENTS 2,078,803 Mayr Apr. 27, 1937' 2,517,435 Jenson Aug. 1, 1950 2,723,367 Book-man Nov. 8, 1955 2,923,800 Borde et al. Feb. 2, 1960 

